# Homework Help: Calculating work from E-Field Graphs

1. Jul 17, 2012

### xSnoopy

1. The problem statement, all variables and given/known data
a)Calculate the work performed by an external agent to move a charge of -0.39x10^-12 C from i' to b'

Hint: The equipotential lines shown are separated by 1 kV. Work to move a charge is the increase in potential energy of the charge. The potential energy is the potential times the charge.

b)Calculate the magnitude of the electric field at `k'.

2. Relevant equations
a)-q*ΔV = Work
b) E = -ΔV/Δd

3. The attempt at a solution
a)I have tried simply plugging in the values:
q = (-0.39x10^-12) and ΔV = ([3 - +3]*1000)

And got the answer 2.34*10^-9 J

b)not really sure where to start here...

2. Jul 17, 2012

### TSny

Hi xSnoopy. Look at the equipotential lines plot and pick an appropriate interval of distance Δd. You'll need to decide where to choose the location of Δd and what direction to orient it. You can then use the ruler in the diagram to estimate Δd in centimeters. Decide how to use this to estimate E.